Assays for TSE agents vary substantially in sensitivity, range of agents detected and time required to detect agents. More promising assay methods should be optimized for use in TSE-agent surveillance programs. Transgenic (Tg) mice expressing the prion-protein genes of more susceptible species show great promise as assay animals for detecting the agents of transmissible spongiform encephalopathies (TSEs). The Laboratory of Method Development, DVP, OVRR, CBER has proposed to establish a program to compare the sensitivity of candidate lines of Tg mice to detect various TSE agents. We will obtain (from collaborators in NIAID) PrP-knock-out mice into which transgenes expressing ovine, bovine or human prion-protein open reading frames including one or more of those mutations thought to increase susceptibility to TSE agents and linked to neuron-specific promoter genes--will be introduced. This must be a long-term effort. In FY 97 and 98 three reference strains of scrapie agent and one of mouse-adapted Creutzfeldt-Jakob disease agent were obtained and archived. In FY 99 working stocks of two strains of scrapie were prepared and titrated in support of this study. Permission was recently granted by investigators at the Institute for Animal Health, Edinburgh to obtain Tg mice derived from their PrP-knockout" progenitors and further engineered by NIAID investigators. A protocol to receive, breed and test susceptibility of a least two lines of mice from NIAID is under review by the CBER Institutional Animal Care and Use Committee. The protocol has been favorably reviewed by CBER's Division of Veterinary Services, and we anticipate final approval early in FY 00. An Animal Study Protocol for preparation and titration of a working stock of the mouse-adapted CJD agent has also undergone preliminary review by CBER's Division of Veterinary Services. This project will be continued in FY 00.